This invention relates to improved structure of a cutoff valve and full-tank detection means provided in a tank, which is suitably adapted to fuel tank of an automobile.
A vaporized-fuel circulation system, called an evaporation circuit, is provided in the vicinity of a fuel tank of an automobile. Vaporized fuel is fed from the fuel tank to an external canister by this evaporation circuit, and is adsorbed by activated carbon or the like to be temporarily stored therein, thereby preventing the increase of an internal pressure of the fuel tank due to the increase of the vapor pressure. The canister is connected to an engine, and the vaporized fuel is expelled from the activated carbon by a negative intake pressure of the engine, and is mixed with a fuel-air mixture, and the adsorbed vaporized fuel is thus again used as the fuel.
In this evaporation circuit, naturally, an opening, called an evaporation opening, is formed in the fuel tank. Generally, this evaporation opening is formed in an uppermost portion of the fuel tank in order to prevent liquid fuel from flowing into the evaporation circuit. However, there is a fear that the liquid fuel flows into the evaporation opening when the liquid level of the fuel moves up and down. If the liquid fuel flowed as far as the canister, this liquid fuel would be adsorbed by the activated carbon, so that the adsorption of the vaporized fuel by the activated carbon would be adversely affected.
Therefore, a cutoff valve has heretofore been provided at the evaporation opening. In many cases, a float valve is used as the cutoff valve as described later. When the liquid level of the fuel rises beyond a predetermined normal level, the float valve floats up because of its buoyancy to close the evaporation opening, thereby preventing the liquid fuel from flowing into the evaporation circuit.
Full-tank detection means for detecting the filling-up of the fuel tank at the time of refueling is provided at the fuel tank. In many cases, this full-tank detection means comprises a float valve as described later, and this float valve closes an opening in the fuel tank so as to increase the internal pressure of the fuel tank, thereby automatically stopping the operation of a refueling gun.
For example, JP-A-11-229984 discloses a device which comprises a shut-off valve for flowing gas, containing fuel vapor produced in a large amount at the time of refueling, to a canister, and a cutoff valve for flowing the gas, containing the fuel vapor, to the canister during the time when the refueling is not effected.
This device is provided at an upper wall of the fuel tank, and comprises an upper housing 100 and a lower housing 200 as shown in FIG. 8. The upper housing 100 is in communication with the canister (not shown). The upper housing 100 and the lower housing 200 communicate with each other via a first communication passage 101 of a smaller diameter and a second communication passage 102 of a larger diameter.
A first float 201 and a second float 202 are provided in the lower housing 200, and the first float 201 is provided in a first space 201a of a tubular shape, and the second float 202 is provided in a second space 202a of an annular shape formed around the first space 201a in isolated relation thereto. The second float 202 is formed into a tubular shape.
The first float 201 has a valve member 201b formed at its upper end, and the second float 202 has a valve member 202b formed at its upper end, and when the liquid level of the fuel moves up and down, the valve member 201b closes and opens the first communication passage 101, and also the valve member 202b closes and opens the second communication passage 102. The first float 201 and the second float 202 are urged upward by springs 203 and 204, respectively, but before the first float 201 or the second float 202 is floated up by the liquid fuel, the valve member 201b or the valve member 202b opens the first communication passage 101 or the second communication passage 102.
A small hole 205 is formed in an upper portion of the lower housing 200, and the first space 201a communicates with a gas phase portion of the fuel tank via the small hole 205. Further, communication holes 206 are formed in bottom portions of the first and second spaces 201a and 202a, respectively, and each of the first and second spaces 201a and 202a communicates with the interior of the fuel tank via the corresponding communication hole 206. The lower housing 200 includes a central tubular portion 207, which extends downwardly from the first space 201a, and is open to a lower end of this lower housing, and an annular tubular portion 208 which extends downwardly from the second space 202a in surrounding relation to the central tubular portion 207, and is open to the lower end of this lower housing.
In this device, in the case where the liquid level of the fuel is disposed at a position 300 lower than the lower end of the lower housing 200, the vaporized fuel enters the first space 201a and the second space 202a via the respective communication holes 206, and flows through the first and second communication passages 101 and 102 into the canister via the upper housing 100. Also, there is another flow of vaporized fuel which enters the first space 201a via the small hole 205, and flows into the canister via the first communication passage 101 and the upper housing 100. As a result, the internal pressure of the fuel tank will not increase, and therefore the refueling operation proceeds smoothly.
Then, after the liquid level of the fuel reaches a position 301 of the lower end of the lower housing 200, the pressure within the central tubular portion 207 becomes higher than the pressure within the fuel tank, and therefore the liquid level of the fuel rises only within the annular tubular portion 208, and the fuel enters the second space 202a through the communication hole 206 to float the second float 202. When the second float 202 thus floats, so that the valve member 202b closes the second communication passage 102, the pressure within the fuel tank abruptly increases, so that an automatic stop function of a refueling gun is exercised, thereby stopping the refueling. Therefore, the filling-up of the fuel tank can be detected.
When the liquid surface of the fuel is disturbed to rise, for example, during the travel of the car, the second float 202 first floats up to close the second communication passage 102, thereby preventing the liquid fuel from flowing into the upper housing 100. When the liquid surface is more vigorously disturbed to rise, the first float 201 also floats up to close the first communication passage 101, thereby preventing the liquid fuel from flowing into the upper housing 100.
In the above device, there are provided the two float valves and the two communication passages, and therefore there is encountered a problem that it is difficult to design the device in such a manner that each of the two float valves can operate accurately. There is another disadvantage that the cost is high since the number of the component parts is rather large. And, the second float 202 and the second space 202a are large in diameter, and this invites a problem that the mounting space is much limited.
Furthermore, in the case where this device is used in fuel tanks of different shapes and capacities, it is necessary to produce many kinds of lower housings 200 and second floats 202, having different shapes, and this invites a problem that much time and labor are required,